Mucinous degenerative change was observed in the epithelial cells lining the renal pelvis, ureter, and urinary bladder of pigs with exudative epidermitis, coliform enteritis, hog cholera, and suppurative arthritis. Mucins were observed within transitional cells either as granular or homogenous material within vacuoles. Lakes filled with mucins also were formed as a result of the coalescence of mucin from degenerating transitional cells. The cells and lakes of mucin were stained selectively by periodic acid-Schiff, alcian blue, and colloidal iron. On the basis of the reactivity patterns with these stains the transitional epithelial cells were considered capable of producing acidic and neutral mucins.